Filming on the set of “The Prince” abruptly came to a screaming halt…literally!… when a fight scene between the flick’s stars – BRUCE WILLIS and JOHN CUSACK – went horribly wrong and Bruce ended up bloody!

Even though a stuntman had choreographed the scene for maximum safety, someone zigged when they should have zagged and John’s fist clipped Bruce’s mouth – not only cutting his lip, but chipping a tooth because he was wearing a ring.

“Bruce was so pissed off,” reports My SpyWitness. “He grabbed his mouth as the blood dripped, screamed for a towel – then screamed at Cusack, ‘I’m too old to be getting beat up like this! Why don’t you just follow the directions they give you – instead of doing whatever the f*** you want!’ John was very apologetic, but because Bruce was so upset, he backed off arguing over whose fault it really was!”

After an hour of applying ice to Bruce’s boo-boo, the swelling subsided, makeup was reapplied and the stars successfully zigzagged through the scene like the old pros they are!